emergency oxygen system is automaticallyactivated during ejection by a lanyard connectedto the cockpit floor. An oxygen/communicationshose is connected to unions on the LH rear topof the lid assembly, and provides connectionsbetween the seat occupant and the aircraft andsurvival kit systems.RADIO LOCATOR BEACON. A URT-33A radio locator beacon is located in a cutoutin the left thigh support. The beacon is actuatedduring ejection by a lanyard connected to acommon anchorage point with the emergencyoxygen lanyard.RUCKSACK ASSEMBLY. The rucksackassembly is attached to the underside of the lidassembly by five fabric straps and a double coneand pin release system. The rucksack contains alife raft and the survival aids. Yellow manualdeployment handles mounted on the kit enablethe occupant to deploy the rucksack and contentsonto a lowering line after seat/man separation.The LRU-23/P life raft inflates automatically onrucksack assembly deployment.COMPONENT OPERATIONThe operation of each component andsubsystem is discussed in the followingparagraphs. The operation of the system as awhole is discussed later in the chapter.Catapult AssemblyExplosive charges are contained in an ejectiongun initiator, JAU-56/A (figs. 5-3 and 5-4), anda secondary cartridge. Gas pressure from the seatfiring system or the aircraft command sequencingsystem operates twin firing pins in the ejection guninitiator to fire the explosive charge.Gas enters the manifold valve through one orboth of the inlet ports, depresses the check valves,and passes down through the vertical bore intothe initiator. Gas pressure acts upon the twinfiring pins in the initiator, shearing the shear pinsand forcing the firing pins down to strike thepercussion caps and ignite the explosive filling.The gas pressure generated within the catapult1. Passes to the ballistic latches to operate thepistons, which retain the multipurpose initiatorstatic lanyards.2. Propels the catapult piston upwards.The initial movement of the piston forces thespring-loaded top latch plunger out of the breechgroove back into the barrel latch (fig. 5-4). Thepiston continues to rise, thrusting against the topcrossbeam of the seat, the upward movementcausing the shaped end of the top latch plungerto ride out of, and disengage from, the barrellatch. Further upward movement of the pistonuncovers the secondary cartridge, which is firedby the pressure and heat of the initiator gas. Afterapproximately 38 inches (965mm) of travel, thepiston head strikes the guide bushing and shearsthe three dowel screws. After a further 4 inches(101mm) of travel, the piston separates from thebarrel and moves away with the ejected seat.Main Beams AssemblyThe main beams assembly supports the majorcomponents of the ejection seat. The operationof the components supported by the main beamsassembly is discussed in the following paragraphs.SHOULDER HARNESS CONTROL SYS-TEM. When the ejection control handle ispulled, gas from the RH seat initiation system ispiped into the breech to operate the cartridge. Thegas also passes to the operating piston in thegovernor housing, forcing it upwards to operatethe trip lever and bring the locking pawl intocontact with the ratchet wheel.The gas from the impulse cartridge in thebreech impinges on the end of the piston forcingit along the cylinder. Horizontal movement of thepiston is transmitted via the threaded drive screwto rotate the splined shaft, spool assemblies, andratchet wheel, which winds in the webbing strapsto pull back and restrain the occupants shoulders.The engaged locking pawl locks the spools in therestrained position.Withdrawal of the webbing straps at excessivespeed causes the two governor pawls to rotateoutwards under centrifugal force and engage theteeth on the housing, preventing rotation of thesplined shaft and spool assemblies and furtherwithdrawal of the straps. This system prevents theoccupant from being thrown forward on crashlanding or sudden deceleration if the shoulderharness control lever is in the disengaged position.Easing of tension on the webbing straps allowsthe pawl springs to reassert themselves anddisengage the pawls from the teeth, permitting freewithdrawal of the straps again.PARACHUTE DEPLOYMENT ROCKETMOTOR. Upon seat ejection, gas pressure from5-26